New Cloth Media Filter System Replace 4 MGD Traveling Bridge Filters with 12 MGD Capacity in Existing Tankage

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Courtesy of Water Environment Federation (WEF)

The Little Falls Run Wastewater Treatment Facility began experiencing operational difficulties with the dual-bay traveling bridge filter process as flows approached the rated capacity for the filters. Although initially the Utilities Department staff intended to duplicate the original filter process and thereby double the capacity, the recent introduction of a cloth media filter product designed to retrofit traveling bridge filters provided the opportunity to install filters with substantially greater capacity within the existing tankage and reserve valuable treatment facility space for future capacity increases.

Following a successful pilot test and approval by the Virginia Department of Environmental Quality, the project was re-designed for the Aqua-Diamond filters. Replacement of the first filter cell was completed within six weeks and followed by a rigid performance and reliability test period. Results from this and subsequent testing have demonstrated the greatly improved efficiency of the cloth media filters over the previous traveling bridge sand media filters.

Stafford County, Virginia is located approximately 40 miles south of Washington, D.C. and has experienced consistently high growth rates for over twenty years. As a result, the Department of Utilities has constructed and repeatedly expanded the two wastewater treatment facilities servicing the county.

The Little Falls Run Wastewater Treatment Facility, located in Stafford County, Virginia was first placed in operation in 1991. The facility (Photo #1) was equipped with a headworks, lowload counter-current (“Schreiber”) aeration process, and circular clarifiers, all rated at 8 million gallons per day (mgd).

As flows to the filters approached 3 gpm/ft2, operating staff were forced to bypass a portion of the flow directly to the ultraviolet disinfection system. Furthermore, backwash frequency increased markedly and treatment performance suffered. While the treatment facility was never at risk of violating the 9 mg/l TSS, 9 mg/l BOD and 2 mg/l total phosphorus limits, the certainty of higher flows and stricter permit limits in the near future meant that immediate tertiary filter improvements were necessary.

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